Recently, the development of backbone communication lines mainly based on optical fiber communication technologies is proceeding steadily and, in such a situation, the transmission speeds of electric signals in electrical devices and information terminals are becoming a bottleneck. Against such background, instead of the conventional electric circuit substrate in which all signal transmissions are made by using the electric signal, the optoelectronic composite substrate of the type that transmits high-speed parts by the light has been proposed, in order to compensate the limit of transmission speed of the electric signal.
In the optoelectronic composite substrate, a light signal is transmitted by an optical waveguide which is constructed such that a core layer is surrounded by cladding layers. Then, the light which is propagated through the core layer is reflected in the vertical direction by a light path conversion mirror which is provided to the end part of the optical waveguide to thereby convert the light path.
A related art is disclosed in Japanese Laid-open Patent Publication No. 2009-180794, Japanese Laid-open Patent Publication No. 2011-75688.